Various plasma processings such as, for example, dry etching, oxidation, and film formation, are performed on a substrate, in manufacturing various electronic devices that are so-called semiconductor devices. In such plasma processings, a plasma processing apparatus is used that generates plasma of a processing gas.
The plasma processing apparatus typically includes a processing container, a susceptor, an electrostatic chuck, first and second high frequency power supplies, and a gas supply unit. The processing container provides an internal space that can be evacuated. The gas supply unit supplies a processing gas to the space within the processing container. The susceptor and the electrostatic chuck are provided within the processing container.
The electrostatic chuck is provided on the susceptor. The electrostatic chuck is configured to attract and hold a substrate placed thereon. Specifically, the electrostatic chuck has an electrode in a dielectric film provided therein. The substrate is held on the electrostatic chuck by the electrostatic force that is generated when a positive polarity DC voltage is applied to the electrode.
In addition, through holes are formed in the susceptor and the electrostatic chuck to move lift pins upward and downward therethrough. The lift pins support the unprocessed substrate on tip ends thereof in a state in which the tip ends protrude to the upper side of the electrostatic chuck. Then, the lift pins move downward such that the substrate is placed on the electrostatic chuck. After the plasma processing of the substrate, the lift pins are moved upward such that the substrate is released from the electrostatic chuck.
A first flow path for a coolant is provided inside the susceptor in order to control the temperature of the substrate during the plasma processing. In addition, for example, a heater device to heat the substrate is provided in the electrostatic chuck. In order to effectively transfer the temperature of the susceptor to the substrate, a second flow path is formed in the susceptor and the electrostatic chuck so as to supply a backside gas for heat transfer (generally, He gas) to the gap between the rear surface of the substrate and the top surface of the electrostatic chuck.
In general, the susceptor also serves as a high frequency electrode, i.e., a lower electrode. A high frequency wave is supplied to the susceptor from the first and second high frequency power supplies through a matcher, during the plasma processing. The first high frequency power supply generates a first high frequency wave for plasma generation, and the second high frequency power supply generates a second high frequency wave for ion drawing-in. When performing the plasma processing, a processing gas is supplied from the gas supply unit into the processing container, and the high frequency waves are supplied from the first and second high frequency power supplies to the susceptor in the state in which the substrate is attracted on the electrostatic chuck, so that plasma of the processing gas is generated.
However, in the plasma processing apparatus, when a high-pressure positive polarity DC voltage is applied to the electrode within the electrostatic chuck, abnormal discharge may occur between the substrate and the susceptor, thereby damaging the substrate. Herein, this phenomenon will be specifically described with reference to FIG. 1. As illustrated in FIG. 1, in general, an electrostatic chuck ESC is provided on the susceptor LE via an adhesive AH. The substrate W is placed on the electrostatic chuck ESC, and a focus ring FR is provided around the substrate W and the electrostatic chuck ESC.
The substrate W is attracted onto the electrostatic chuck ESC by the electrostatic force that is generated when the positive polarity DC voltage is applied to the electrode CE of the electrostatic chuck ESC from a DC power supply DCP. In the state illustrated in FIG. 1, the electrostatic chuck ESC has a potential of a high positive polarity, for example, a potential of 1,000 V or more, as represented by + that is superimposed on the electrostatic chuck ESC in FIG. 1. In addition, it may be regarded that the susceptor LE is in a state of electrically floating with respect to the grounded processing container, and a capacitance (represented as the reference code CA in FIG. 1) exists between the susceptor LE and the processing container. Further, it may be regarded that a capacitance (represented as the reference symbol CB in FIG. 1) also exists between the susceptor LE and the electrode CE of the electrostatic chuck ESC. Accordingly, the susceptor LE has a potential of the same polarity as that of the electrostatic chuck ESC, i.e., the positive polarity, as represented by + that is superimposed on the susceptor LE in FIG. 1. When the high frequency waves from the first and the second frequency power supplies are applied to the susceptor for plasma generation, the substrate W is exposed to the plasma, and the potential of the substrate W falls to be equal to or lower than a negative polarity potential (e.g., −500 V), which is identical to self-bias, as represented by − that is superimposed on the substrate W in FIG. 1. As a result, a large potential difference occurs between the substrate W and the susceptor LE.
In addition, as described above, the second flow path for the backside gas and a space DS corresponding to the through holes for the lift pins are formed in the susceptor LE and the electrostatic chuck ESC. Since a gas may exist within the space DS, abnormal discharge (see arrow A in FIG. 1) may occur between the substrate W and the susceptor LE due to the potential difference as described above.
In order to suppress such abnormal discharge, Japanese Patent Laid-Open Publication No. 2011-210958 discloses a technology that provides a current limiting device between a focus ring having a potential substantially equal to that of a substrate and a susceptor to move charges between the susceptor and the focus ring through the current limiting device so as to make the potential of the susceptor and the potential of the substrate close to each other.